1. Field of the Invention
The present invention relates to a light source unit and a projector which includes the light source unit.
2. Description of the Related Art
Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-341105), for example, proposes a light source unit having a light emitting diode which functions as an excitation light source and a luminescent wheel in which luminescent material layers are formed on a transparent base material for converting ultraviolet light emitted from the excitation light source into visible light.
The proposal made in Patent Document 1 is a configuration in which light rays of red, green and blue wavelength bands can be emitted sequentially by rotating the luminescent wheel. This requires excitation light to be shone continuously onto red, green and blue luminescent light emitting areas on a surface of the luminescent wheel, which requires, in turn, the excitation light source to be driven at all times, leading to a problem that the life of the excitation light source is shortened due to heat generated therein as a result of the continuous driving thereof. To cope with this problem, the driving output of the excitation light source needs to be suppressed so as to suppress, in turn, an increase in temperature of the excitation light source. In addition, due to the configuration in which the red, green and blue luminescent light rays are emitted sequentially from the corresponding luminescent light emitting areas which are formed on the luminescent wheel, it is not possible to enhance the luminance of an image by producing white light or light of a wavelength band of a highly pure complementary color through combination of the light rays of the respective colors. Further, in this proposal, since the red, green and blue light rays emitted from the corresponding luminescent light emitting areas are controlled with time sharing, the rotation of a wheel motor needs to be controlled.
Since the luminous efficiency of red, green and blue light rays which are emitted from the corresponding luminescent light emitting areas largely depends on the physical properties of the luminescent materials used, there is caused a problem that it is difficult to display on a screen an image which is superior in color balance.
It is also possible to propose a light source unit which has a plurality of types of semiconductor light emitting devices so that red, green and blue light rays can be produced by corresponding light emitting diodes. In the case of this configuration being adopted, however, the luminous efficiency of a green semiconductor light emitting device is lower than those of red and blue semiconductor light emitting devices, leading to a problem that it is difficult to obtain light source light with a high luminance.